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<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2007 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License");<a name="line.4"></a>
<span class="sourceLineNo">005</span> * you may not use this file except in compliance with the License.<a name="line.5"></a>
<span class="sourceLineNo">006</span> * You may obtain a copy of the License at<a name="line.6"></a>
<span class="sourceLineNo">007</span> *<a name="line.7"></a>
<span class="sourceLineNo">008</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.8"></a>
<span class="sourceLineNo">009</span> *<a name="line.9"></a>
<span class="sourceLineNo">010</span> * Unless required by applicable law or agreed to in writing, software<a name="line.10"></a>
<span class="sourceLineNo">011</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.11"></a>
<span class="sourceLineNo">012</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.12"></a>
<span class="sourceLineNo">013</span> * See the License for the specific language governing permissions and<a name="line.13"></a>
<span class="sourceLineNo">014</span> * limitations under the License.<a name="line.14"></a>
<span class="sourceLineNo">015</span> */<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>package com.google.common.base;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>import static com.google.common.base.Preconditions.checkArgument;<a name="line.19"></a>
<span class="sourceLineNo">020</span>import static com.google.common.base.Preconditions.checkNotNull;<a name="line.20"></a>
<span class="sourceLineNo">021</span><a name="line.21"></a>
<span class="sourceLineNo">022</span>import com.google.common.annotations.Beta;<a name="line.22"></a>
<span class="sourceLineNo">023</span>import com.google.common.annotations.GwtCompatible;<a name="line.23"></a>
<span class="sourceLineNo">024</span><a name="line.24"></a>
<span class="sourceLineNo">025</span>import java.io.Serializable;<a name="line.25"></a>
<span class="sourceLineNo">026</span>import java.util.Map;<a name="line.26"></a>
<span class="sourceLineNo">027</span><a name="line.27"></a>
<span class="sourceLineNo">028</span>import javax.annotation.Nullable;<a name="line.28"></a>
<span class="sourceLineNo">029</span><a name="line.29"></a>
<span class="sourceLineNo">030</span>/**<a name="line.30"></a>
<span class="sourceLineNo">031</span> * Static utility methods pertaining to {@code Function} instances.<a name="line.31"></a>
<span class="sourceLineNo">032</span> *<a name="line.32"></a>
<span class="sourceLineNo">033</span> * &lt;p&gt;All methods return serializable functions as long as they're given serializable parameters.<a name="line.33"></a>
<span class="sourceLineNo">034</span> * <a name="line.34"></a>
<span class="sourceLineNo">035</span> * &lt;p&gt;See the Guava User Guide article on &lt;a href=<a name="line.35"></a>
<span class="sourceLineNo">036</span> * "http://code.google.com/p/guava-libraries/wiki/FunctionalExplained"&gt;the use of {@code<a name="line.36"></a>
<span class="sourceLineNo">037</span> * Function}&lt;/a&gt;.<a name="line.37"></a>
<span class="sourceLineNo">038</span> *<a name="line.38"></a>
<span class="sourceLineNo">039</span> * @author Mike Bostock<a name="line.39"></a>
<span class="sourceLineNo">040</span> * @author Jared Levy<a name="line.40"></a>
<span class="sourceLineNo">041</span> * @since 2.0 (imported from Google Collections Library)<a name="line.41"></a>
<span class="sourceLineNo">042</span> */<a name="line.42"></a>
<span class="sourceLineNo">043</span>@GwtCompatible<a name="line.43"></a>
<span class="sourceLineNo">044</span>public final class Functions {<a name="line.44"></a>
<span class="sourceLineNo">045</span>  private Functions() {}<a name="line.45"></a>
<span class="sourceLineNo">046</span><a name="line.46"></a>
<span class="sourceLineNo">047</span>  /**<a name="line.47"></a>
<span class="sourceLineNo">048</span>   * Returns a function that calls {@code toString()} on its argument. The function does not accept<a name="line.48"></a>
<span class="sourceLineNo">049</span>   * nulls; it will throw a {@link NullPointerException} when applied to {@code null}.<a name="line.49"></a>
<span class="sourceLineNo">050</span>   *<a name="line.50"></a>
<span class="sourceLineNo">051</span>   * &lt;p&gt;&lt;b&gt;Warning:&lt;/b&gt; The returned function may not be &lt;i&gt;consistent with equals&lt;/i&gt; (as<a name="line.51"></a>
<span class="sourceLineNo">052</span>   * documented at {@link Function#apply}). For example, this function yields different results for<a name="line.52"></a>
<span class="sourceLineNo">053</span>   * the two equal instances {@code ImmutableSet.of(1, 2)} and {@code ImmutableSet.of(2, 1)}.<a name="line.53"></a>
<span class="sourceLineNo">054</span>   */<a name="line.54"></a>
<span class="sourceLineNo">055</span>  public static Function&lt;Object, String&gt; toStringFunction() {<a name="line.55"></a>
<span class="sourceLineNo">056</span>    return ToStringFunction.INSTANCE;<a name="line.56"></a>
<span class="sourceLineNo">057</span>  }<a name="line.57"></a>
<span class="sourceLineNo">058</span><a name="line.58"></a>
<span class="sourceLineNo">059</span>  // enum singleton pattern<a name="line.59"></a>
<span class="sourceLineNo">060</span>  private enum ToStringFunction implements Function&lt;Object, String&gt; {<a name="line.60"></a>
<span class="sourceLineNo">061</span>    INSTANCE;<a name="line.61"></a>
<span class="sourceLineNo">062</span><a name="line.62"></a>
<span class="sourceLineNo">063</span>    @Override<a name="line.63"></a>
<span class="sourceLineNo">064</span>    public String apply(Object o) {<a name="line.64"></a>
<span class="sourceLineNo">065</span>      checkNotNull(o);  // eager for GWT.<a name="line.65"></a>
<span class="sourceLineNo">066</span>      return o.toString();<a name="line.66"></a>
<span class="sourceLineNo">067</span>    }<a name="line.67"></a>
<span class="sourceLineNo">068</span><a name="line.68"></a>
<span class="sourceLineNo">069</span>    @Override public String toString() {<a name="line.69"></a>
<span class="sourceLineNo">070</span>      return "toString";<a name="line.70"></a>
<span class="sourceLineNo">071</span>    }<a name="line.71"></a>
<span class="sourceLineNo">072</span>  }<a name="line.72"></a>
<span class="sourceLineNo">073</span><a name="line.73"></a>
<span class="sourceLineNo">074</span>  /**<a name="line.74"></a>
<span class="sourceLineNo">075</span>   * Returns the identity function.<a name="line.75"></a>
<span class="sourceLineNo">076</span>   */<a name="line.76"></a>
<span class="sourceLineNo">077</span>  @SuppressWarnings("unchecked")<a name="line.77"></a>
<span class="sourceLineNo">078</span>  public static &lt;E&gt; Function&lt;E, E&gt; identity() {<a name="line.78"></a>
<span class="sourceLineNo">079</span>    return (Function&lt;E, E&gt;) IdentityFunction.INSTANCE;<a name="line.79"></a>
<span class="sourceLineNo">080</span>  }<a name="line.80"></a>
<span class="sourceLineNo">081</span><a name="line.81"></a>
<span class="sourceLineNo">082</span>  // enum singleton pattern<a name="line.82"></a>
<span class="sourceLineNo">083</span>  private enum IdentityFunction implements Function&lt;Object, Object&gt; {<a name="line.83"></a>
<span class="sourceLineNo">084</span>    INSTANCE;<a name="line.84"></a>
<span class="sourceLineNo">085</span><a name="line.85"></a>
<span class="sourceLineNo">086</span>    @Override<a name="line.86"></a>
<span class="sourceLineNo">087</span>    @Nullable<a name="line.87"></a>
<span class="sourceLineNo">088</span>    public Object apply(@Nullable Object o) {<a name="line.88"></a>
<span class="sourceLineNo">089</span>      return o;<a name="line.89"></a>
<span class="sourceLineNo">090</span>    }<a name="line.90"></a>
<span class="sourceLineNo">091</span><a name="line.91"></a>
<span class="sourceLineNo">092</span>    @Override public String toString() {<a name="line.92"></a>
<span class="sourceLineNo">093</span>      return "identity";<a name="line.93"></a>
<span class="sourceLineNo">094</span>    }<a name="line.94"></a>
<span class="sourceLineNo">095</span>  }<a name="line.95"></a>
<span class="sourceLineNo">096</span><a name="line.96"></a>
<span class="sourceLineNo">097</span>  /**<a name="line.97"></a>
<span class="sourceLineNo">098</span>   * Returns a function which performs a map lookup. The returned function throws an {@link<a name="line.98"></a>
<span class="sourceLineNo">099</span>   * IllegalArgumentException} if given a key that does not exist in the map.<a name="line.99"></a>
<span class="sourceLineNo">100</span>   */<a name="line.100"></a>
<span class="sourceLineNo">101</span>  public static &lt;K, V&gt; Function&lt;K, V&gt; forMap(Map&lt;K, V&gt; map) {<a name="line.101"></a>
<span class="sourceLineNo">102</span>    return new FunctionForMapNoDefault&lt;K, V&gt;(map);<a name="line.102"></a>
<span class="sourceLineNo">103</span>  }<a name="line.103"></a>
<span class="sourceLineNo">104</span><a name="line.104"></a>
<span class="sourceLineNo">105</span>  private static class FunctionForMapNoDefault&lt;K, V&gt; implements Function&lt;K, V&gt;, Serializable {<a name="line.105"></a>
<span class="sourceLineNo">106</span>    final Map&lt;K, V&gt; map;<a name="line.106"></a>
<span class="sourceLineNo">107</span><a name="line.107"></a>
<span class="sourceLineNo">108</span>    FunctionForMapNoDefault(Map&lt;K, V&gt; map) {<a name="line.108"></a>
<span class="sourceLineNo">109</span>      this.map = checkNotNull(map);<a name="line.109"></a>
<span class="sourceLineNo">110</span>    }<a name="line.110"></a>
<span class="sourceLineNo">111</span><a name="line.111"></a>
<span class="sourceLineNo">112</span>    @Override<a name="line.112"></a>
<span class="sourceLineNo">113</span>    public V apply(@Nullable K key) {<a name="line.113"></a>
<span class="sourceLineNo">114</span>      V result = map.get(key);<a name="line.114"></a>
<span class="sourceLineNo">115</span>      checkArgument(result != null || map.containsKey(key), "Key '%s' not present in map", key);<a name="line.115"></a>
<span class="sourceLineNo">116</span>      return result;<a name="line.116"></a>
<span class="sourceLineNo">117</span>    }<a name="line.117"></a>
<span class="sourceLineNo">118</span><a name="line.118"></a>
<span class="sourceLineNo">119</span>    @Override public boolean equals(@Nullable Object o) {<a name="line.119"></a>
<span class="sourceLineNo">120</span>      if (o instanceof FunctionForMapNoDefault) {<a name="line.120"></a>
<span class="sourceLineNo">121</span>        FunctionForMapNoDefault&lt;?, ?&gt; that = (FunctionForMapNoDefault&lt;?, ?&gt;) o;<a name="line.121"></a>
<span class="sourceLineNo">122</span>        return map.equals(that.map);<a name="line.122"></a>
<span class="sourceLineNo">123</span>      }<a name="line.123"></a>
<span class="sourceLineNo">124</span>      return false;<a name="line.124"></a>
<span class="sourceLineNo">125</span>    }<a name="line.125"></a>
<span class="sourceLineNo">126</span><a name="line.126"></a>
<span class="sourceLineNo">127</span>    @Override public int hashCode() {<a name="line.127"></a>
<span class="sourceLineNo">128</span>      return map.hashCode();<a name="line.128"></a>
<span class="sourceLineNo">129</span>    }<a name="line.129"></a>
<span class="sourceLineNo">130</span><a name="line.130"></a>
<span class="sourceLineNo">131</span>    @Override public String toString() {<a name="line.131"></a>
<span class="sourceLineNo">132</span>      return "forMap(" + map + ")";<a name="line.132"></a>
<span class="sourceLineNo">133</span>    }<a name="line.133"></a>
<span class="sourceLineNo">134</span><a name="line.134"></a>
<span class="sourceLineNo">135</span>    private static final long serialVersionUID = 0;<a name="line.135"></a>
<span class="sourceLineNo">136</span>  }<a name="line.136"></a>
<span class="sourceLineNo">137</span><a name="line.137"></a>
<span class="sourceLineNo">138</span>  /**<a name="line.138"></a>
<span class="sourceLineNo">139</span>   * Returns a function which performs a map lookup with a default value. The function created by<a name="line.139"></a>
<span class="sourceLineNo">140</span>   * this method returns {@code defaultValue} for all inputs that do not belong to the map's key<a name="line.140"></a>
<span class="sourceLineNo">141</span>   * set.<a name="line.141"></a>
<span class="sourceLineNo">142</span>   *<a name="line.142"></a>
<span class="sourceLineNo">143</span>   * @param map source map that determines the function behavior<a name="line.143"></a>
<span class="sourceLineNo">144</span>   * @param defaultValue the value to return for inputs that aren't map keys<a name="line.144"></a>
<span class="sourceLineNo">145</span>   * @return function that returns {@code map.get(a)} when {@code a} is a key, or {@code<a name="line.145"></a>
<span class="sourceLineNo">146</span>   *         defaultValue} otherwise<a name="line.146"></a>
<span class="sourceLineNo">147</span>   */<a name="line.147"></a>
<span class="sourceLineNo">148</span>  public static &lt;K, V&gt; Function&lt;K, V&gt; forMap(Map&lt;K, ? extends V&gt; map, @Nullable V defaultValue) {<a name="line.148"></a>
<span class="sourceLineNo">149</span>    return new ForMapWithDefault&lt;K, V&gt;(map, defaultValue);<a name="line.149"></a>
<span class="sourceLineNo">150</span>  }<a name="line.150"></a>
<span class="sourceLineNo">151</span><a name="line.151"></a>
<span class="sourceLineNo">152</span>  private static class ForMapWithDefault&lt;K, V&gt; implements Function&lt;K, V&gt;, Serializable {<a name="line.152"></a>
<span class="sourceLineNo">153</span>    final Map&lt;K, ? extends V&gt; map;<a name="line.153"></a>
<span class="sourceLineNo">154</span>    final V defaultValue;<a name="line.154"></a>
<span class="sourceLineNo">155</span><a name="line.155"></a>
<span class="sourceLineNo">156</span>    ForMapWithDefault(Map&lt;K, ? extends V&gt; map, @Nullable V defaultValue) {<a name="line.156"></a>
<span class="sourceLineNo">157</span>      this.map = checkNotNull(map);<a name="line.157"></a>
<span class="sourceLineNo">158</span>      this.defaultValue = defaultValue;<a name="line.158"></a>
<span class="sourceLineNo">159</span>    }<a name="line.159"></a>
<span class="sourceLineNo">160</span><a name="line.160"></a>
<span class="sourceLineNo">161</span>    @Override<a name="line.161"></a>
<span class="sourceLineNo">162</span>    public V apply(@Nullable K key) {<a name="line.162"></a>
<span class="sourceLineNo">163</span>      V result = map.get(key);<a name="line.163"></a>
<span class="sourceLineNo">164</span>      return (result != null || map.containsKey(key)) ? result : defaultValue;<a name="line.164"></a>
<span class="sourceLineNo">165</span>    }<a name="line.165"></a>
<span class="sourceLineNo">166</span><a name="line.166"></a>
<span class="sourceLineNo">167</span>    @Override public boolean equals(@Nullable Object o) {<a name="line.167"></a>
<span class="sourceLineNo">168</span>      if (o instanceof ForMapWithDefault) {<a name="line.168"></a>
<span class="sourceLineNo">169</span>        ForMapWithDefault&lt;?, ?&gt; that = (ForMapWithDefault&lt;?, ?&gt;) o;<a name="line.169"></a>
<span class="sourceLineNo">170</span>        return map.equals(that.map) &amp;&amp; Objects.equal(defaultValue, that.defaultValue);<a name="line.170"></a>
<span class="sourceLineNo">171</span>      }<a name="line.171"></a>
<span class="sourceLineNo">172</span>      return false;<a name="line.172"></a>
<span class="sourceLineNo">173</span>    }<a name="line.173"></a>
<span class="sourceLineNo">174</span><a name="line.174"></a>
<span class="sourceLineNo">175</span>    @Override public int hashCode() {<a name="line.175"></a>
<span class="sourceLineNo">176</span>      return Objects.hashCode(map, defaultValue);<a name="line.176"></a>
<span class="sourceLineNo">177</span>    }<a name="line.177"></a>
<span class="sourceLineNo">178</span><a name="line.178"></a>
<span class="sourceLineNo">179</span>    @Override public String toString() {<a name="line.179"></a>
<span class="sourceLineNo">180</span>      return "forMap(" + map + ", defaultValue=" + defaultValue + ")";<a name="line.180"></a>
<span class="sourceLineNo">181</span>    }<a name="line.181"></a>
<span class="sourceLineNo">182</span><a name="line.182"></a>
<span class="sourceLineNo">183</span>    private static final long serialVersionUID = 0;<a name="line.183"></a>
<span class="sourceLineNo">184</span>  }<a name="line.184"></a>
<span class="sourceLineNo">185</span><a name="line.185"></a>
<span class="sourceLineNo">186</span>  /**<a name="line.186"></a>
<span class="sourceLineNo">187</span>   * Returns the composition of two functions. For {@code f: A-&gt;B} and {@code g: B-&gt;C}, composition<a name="line.187"></a>
<span class="sourceLineNo">188</span>   * is defined as the function h such that {@code h(a) == g(f(a))} for each {@code a}.<a name="line.188"></a>
<span class="sourceLineNo">189</span>   *<a name="line.189"></a>
<span class="sourceLineNo">190</span>   * @param g the second function to apply<a name="line.190"></a>
<span class="sourceLineNo">191</span>   * @param f the first function to apply<a name="line.191"></a>
<span class="sourceLineNo">192</span>   * @return the composition of {@code f} and {@code g}<a name="line.192"></a>
<span class="sourceLineNo">193</span>   * @see &lt;a href="//en.wikipedia.org/wiki/Function_composition"&gt;function composition&lt;/a&gt;<a name="line.193"></a>
<span class="sourceLineNo">194</span>   */<a name="line.194"></a>
<span class="sourceLineNo">195</span>  public static &lt;A, B, C&gt; Function&lt;A, C&gt; compose(Function&lt;B, C&gt; g, Function&lt;A, ? extends B&gt; f) {<a name="line.195"></a>
<span class="sourceLineNo">196</span>    return new FunctionComposition&lt;A, B, C&gt;(g, f);<a name="line.196"></a>
<span class="sourceLineNo">197</span>  }<a name="line.197"></a>
<span class="sourceLineNo">198</span><a name="line.198"></a>
<span class="sourceLineNo">199</span>  private static class FunctionComposition&lt;A, B, C&gt; implements Function&lt;A, C&gt;, Serializable {<a name="line.199"></a>
<span class="sourceLineNo">200</span>    private final Function&lt;B, C&gt; g;<a name="line.200"></a>
<span class="sourceLineNo">201</span>    private final Function&lt;A, ? extends B&gt; f;<a name="line.201"></a>
<span class="sourceLineNo">202</span><a name="line.202"></a>
<span class="sourceLineNo">203</span>    public FunctionComposition(Function&lt;B, C&gt; g, Function&lt;A, ? extends B&gt; f) {<a name="line.203"></a>
<span class="sourceLineNo">204</span>      this.g = checkNotNull(g);<a name="line.204"></a>
<span class="sourceLineNo">205</span>      this.f = checkNotNull(f);<a name="line.205"></a>
<span class="sourceLineNo">206</span>    }<a name="line.206"></a>
<span class="sourceLineNo">207</span><a name="line.207"></a>
<span class="sourceLineNo">208</span>    @Override<a name="line.208"></a>
<span class="sourceLineNo">209</span>    public C apply(@Nullable A a) {<a name="line.209"></a>
<span class="sourceLineNo">210</span>      return g.apply(f.apply(a));<a name="line.210"></a>
<span class="sourceLineNo">211</span>    }<a name="line.211"></a>
<span class="sourceLineNo">212</span><a name="line.212"></a>
<span class="sourceLineNo">213</span>    @Override public boolean equals(@Nullable Object obj) {<a name="line.213"></a>
<span class="sourceLineNo">214</span>      if (obj instanceof FunctionComposition) {<a name="line.214"></a>
<span class="sourceLineNo">215</span>        FunctionComposition&lt;?, ?, ?&gt; that = (FunctionComposition&lt;?, ?, ?&gt;) obj;<a name="line.215"></a>
<span class="sourceLineNo">216</span>        return f.equals(that.f) &amp;&amp; g.equals(that.g);<a name="line.216"></a>
<span class="sourceLineNo">217</span>      }<a name="line.217"></a>
<span class="sourceLineNo">218</span>      return false;<a name="line.218"></a>
<span class="sourceLineNo">219</span>    }<a name="line.219"></a>
<span class="sourceLineNo">220</span><a name="line.220"></a>
<span class="sourceLineNo">221</span>    @Override public int hashCode() {<a name="line.221"></a>
<span class="sourceLineNo">222</span>      return f.hashCode() ^ g.hashCode();<a name="line.222"></a>
<span class="sourceLineNo">223</span>    }<a name="line.223"></a>
<span class="sourceLineNo">224</span><a name="line.224"></a>
<span class="sourceLineNo">225</span>    @Override public String toString() {<a name="line.225"></a>
<span class="sourceLineNo">226</span>      return g.toString() + "(" + f.toString() + ")";<a name="line.226"></a>
<span class="sourceLineNo">227</span>    }<a name="line.227"></a>
<span class="sourceLineNo">228</span><a name="line.228"></a>
<span class="sourceLineNo">229</span>    private static final long serialVersionUID = 0;<a name="line.229"></a>
<span class="sourceLineNo">230</span>  }<a name="line.230"></a>
<span class="sourceLineNo">231</span><a name="line.231"></a>
<span class="sourceLineNo">232</span>  /**<a name="line.232"></a>
<span class="sourceLineNo">233</span>   * Creates a function that returns the same boolean output as the given predicate for all inputs.<a name="line.233"></a>
<span class="sourceLineNo">234</span>   *<a name="line.234"></a>
<span class="sourceLineNo">235</span>   * &lt;p&gt;The returned function is &lt;i&gt;consistent with equals&lt;/i&gt; (as documented at {@link<a name="line.235"></a>
<span class="sourceLineNo">236</span>   * Function#apply}) if and only if {@code predicate} is itself consistent with equals.<a name="line.236"></a>
<span class="sourceLineNo">237</span>   */<a name="line.237"></a>
<span class="sourceLineNo">238</span>  public static &lt;T&gt; Function&lt;T, Boolean&gt; forPredicate(Predicate&lt;T&gt; predicate) {<a name="line.238"></a>
<span class="sourceLineNo">239</span>    return new PredicateFunction&lt;T&gt;(predicate);<a name="line.239"></a>
<span class="sourceLineNo">240</span>  }<a name="line.240"></a>
<span class="sourceLineNo">241</span><a name="line.241"></a>
<span class="sourceLineNo">242</span>  /** @see Functions#forPredicate */<a name="line.242"></a>
<span class="sourceLineNo">243</span>  private static class PredicateFunction&lt;T&gt; implements Function&lt;T, Boolean&gt;, Serializable {<a name="line.243"></a>
<span class="sourceLineNo">244</span>    private final Predicate&lt;T&gt; predicate;<a name="line.244"></a>
<span class="sourceLineNo">245</span><a name="line.245"></a>
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